The invention is based on a device for adjusting the onset of the supply for a fuel injection pump, in particular an in-line injection pump or plug-in pump.
Devices for adjusting the supply onset of this kind have already been known for a long time. In a known fuel injection pump having this kind of device for adjusting the onset of the hydraulic supply (German Auslegeschrift 1 107025), an adjusting piston that can be acted upon by the pressure of a control fluid is present inside the drive tappet. The delivery of the control fluid is done via a conduit arrangement having a delivery conduit in the pump housing. Besides the delivery conduit discharging into a guide bore of the drive tappet, this arrangement has a radial connecting bore, drilled through the wall of the drive tappet, to the pressure chamber of the device for adjusting the onset of the supply. At bottom dead center of the pump piston, these connecting bores face one another, so that the control fluid, which is under control pressure, can flow into the pressure chamber inside the drive tappet. In this known arrangement, the pressure of the control fluid must overcome the initial tension of the tappet spring that loads the adjusting piston. Depending on the magnitude of the fluid pressure, the adjusting piston and simultaneously the pump piston are raised relative to the drive tappet, so that in the ensuing compression stroke and with the previously interrupted communication between the delivery conduit and the connecting bore, an earlier supply onset by the pump piston is controlled than if the fluid pressure had not raised the adjusting piston.
In other known devices of this type (German Offenlegungsschrift 3 409 295, German Patent 3 510 223, German Offenlegungsschrift 3 742 831 and Japanese Patent 47-28016), a forward shift of the injection onset, as is necessary for various engine operating states, is achieved by hydraulically varying the prestroke of the pump piston. Some of these versions necessitate relatively major engineering expense, but on the other hand they also enable only a two-point adjustment of the pump piston. To create an injection onset that can be varied during operation as well as as a function of engine parameters is not made possible by these injection adjusters, since a pressure-dependent, infinitely graduated control has overly large tolerances.